drivers: core: lists: fix for loop index type

drivers: core: lists: fix for loop index type

* fixes the bug in function bind_drivers_pass that for
CONFIG_CC_OPTIMIZE_FOR_SIZE=n and no entries in the driver_info list,
i.e. n_ents == 0, the processor steps into the first loop iteration
despite the loop condition being false.
* the Xilinx Zynq-7000 device would eventually hang due to an attempted
access to an invalid memory address
* the bug is fixed by changing the type of idx from uint to int

Board: zynq-zybo
Target: ARM
Compiler: arm-none-eabi-gcc 9.2.1

Signed-off-by: Alexander Preissner <fpga-garage@preissner-muc.de>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>